Hollow glass microspheres having an average diameter of less than about 500 micrometers, also commonly known as “glass microbubbles”, “glass bubbles”, “hollow glass beads”, or “glass balloons” are widely used in industry, for example, as additives to polymeric compositions. In many industries, hollow glass microspheres are useful, for example, for lowering weight and improving processing, dimensional stability, and flow properties of a polymeric composition. Generally, it is desirable that the hollow glass microspheres be strong enough to avoid being crushed or broken during processing of the particular polymeric compound. Hollow glass microspheres have been incorporated into polypropylene compositions for certain applications. See, for example, U.S. Pat. No. 7,365,144 (Ka et al.).